This invention relates to a method and apparatus to attain uniform development of a film with little difference of the activity of the developer from the leading end to the trailing end of the photographic film when the film is developed by a film processor. By the method and apparatus of the invention, uniform development is achieved by compensating for the decrease of the activity due to the exhaustion of the developer by increasing the length of time the film is immersed in the developer by gradually increasing the surface level of the developer in the developing tank, beginning immediately after the start of the feeding of the film, thus prolonging the time of development.
In development of the photographic films the factors which may affect the density of the developed images on the photographic films are: 1 the activity of the developer, 2 the temperature of the developer, 3 the time of development, 4 the degree of agitation of the developer, etc. In the well-known film processors, such conditions are always maintained constant. However, (a) it is very difficult to keep the activity of the developer constant because the activity changes momentarily with the exhaustion of the developer due to the development of the exposed films. Even if a large amount of the developer is used and the developer is agitated as often as possible to diminish the change of the activity, it is almost impossible to keep the activity of the developer constant, which activity which changes momentarily at every part of the films, e.g. at the leading end or at the trailing end of the films, so as to attain uniform development of photographic films.
In addition, (b) it seems to be advisable to decrease the speed of the films through the developer gradually according to the degree of exhaustion of the developer, but suitable control of the speed of the films is very difficult. Moreover, (c) it is almost impossible to control temperature, that is, to vary the temperature of the liquid in contact with the film appropriately according to the change of the activity of the liquid during the development.
Therefore, it has been the practice to add replenisher in order to maintain the activity of the developer, but so far this has been done for correcting only the average activity of the circulating developer. However, with only such a correction of the activity of the developer it has been impossible to compensate for the difference of the concentration of the developer from the leading end to the trailing end of the film to be treated, as described above. Especially in the development of a film of a large size, the difference of the contrast of the images on the film at the leading part and at the trailing part of the film can not be avoided.
This invention provides a method and an apparatus for the development of the film in a film processor in which the difference of the momentarily changing activity of the developer in contact with the film kept as small as possible, by gradually increasing the length of the film immersed by gradually elevating the surface of the developer from the level of a lower overflow tube according to the difference of the activity occurring during passing of the film to be treated through the developer in the developing tank of the automatic film processor equipped with a supplement tank of the developer and a metering pump, a developing tank to which a higher and a lower overflow tube is attached, and by gradually increasing the time of development from the leading part toward the trailing part of the film. This invention will be described in detail in connection with the drawings in the following.
The said invention makes possible the best compensation by a simple method for the decrease of the concentration of the developer acting on the trailing part of the photographic films due to the exhaustion of the developer, to obtain a uniform development, which is very useful in practice.